PRIMING OF OBJECT CATEGORIZATION WITHIN AND ACROSS LEVELS OF SPECIFICITY

Abstract

Identification of objects can occur at different levels of specificity. Depending on task and context, an object can be classified at the superordinate level (as an animal), at the basic level (a bird) or at the subordinate level (a sparrow). What are the interactions between these representational levels and do they rely on the same sequential processes that lead to successful object identification? In this electroencephalogram study, a task-switching paradigm (covert naming or living/non-living judgment) was used. Images of objects were repeated either within the same task, or with a switch from a covert naming task to a living or non-living judgment and vice versa. While covert naming accesses entry-level (basic or subordinate), living/non-living judgments rely oil superordinate classification. Our beha-vioural results demonstrated clear priming effects within both tasks. However asymmetries were found when task-switching had occurred, with facilitation for covert naming but not for categorization. We also found lower accuracy and early-starting and persistent enhancements Of event-related potentials (ERPs) for covert naming, indicating that this task was more difficult and involved more intense perceptual and semantic processing. Perceptual priming was marked by consistent reductions of the ERP component L1 for repeated presentations, both with and without task switching. Additional repetition effects were found in early event related activity between 150-190 ms (N1) when a repeated image had been named at initial presentation. We conclude that differences in N1 indicate task-related changes in the identification process itself Such enhancements for covert naming again emerge in a later time window associated with depth of semantic processing. Meanwhile, L1 reflects modulations due to implicit memory of objects. In conclusion, evidence was found for representational overlap; changes in ERP markers started early and revealed cross-task priming at the level of object structure analysis and more intense perceptual and semantic processing for covert naming.